Is carbon fiber stronger than steel？

The strength of carbon fiber and steel

Carbon fiber is a carbon-containing organic fiber, in the inert gas, through pre-oxidation and high temperature carbonization and other processes, to form a graphite-like structure, it is this special structure makes carbon fiber to obtain special high performance.

Because the carbon in carbon fiber exists in the form of covalent carbon and is distributed along the lattice axis, it has high strength and high elastic modulus. It is four times stronger than steel, seven times stronger than lead, and 12 times stronger than aluminum. The deformation resistance is more than 2 times larger than steel, and 5 to 6 times larger than glass fiber. Carbon fiber has a wide range of temperature adaptation, and it can withstand both high and low temperatures. At a high temperature of 600℃, its performance remains unchanged, while non-metallic materials such as nylon and glass fiber decrease in strength with increasing temperature; When -180℃, due to the low temperature and cold brittleness, the steel is very brittle, and the carbon fiber cloth still has good flexibility. Carbon fiber has good chemical resistance, it is not as easy to rust as metal, and its diameter and strength will not change after soaking in 50% hydrochloric acid solution for 200 days. The high temperature thermal conductivity of carbon fiber is extremely low, which is 1/10 of that of fireclay.

Performance characteristics:

Carbon fiber has small specific gravity, high tensile strength, high axial strength and modulus, no creep, good fatigue resistance, specific heat and electrical conductivity between non-metal and metal, small thermal expansion coefficient, good corrosion resistance, low fiber density, and good X-ray transmission. However, its impact resistance is poor, easy to damage, oxidation occurs under the action of strong acids, and metal carbonization, carburizing and electrochemical corrosion occur when it is combined with metal. Therefore, the carbon fiber must be surface treated before use. In short, carbon fiber is a new material with excellent mechanical properties.

Application field:

The aircraft made of composite materials made of carbon fiber and plastic is not only lightweight, but also consumes less power, has large thrust and has low noise; Using carbon fiber to make the disk of electronic computer can improve the storage capacity and operation speed of computer. The use of carbon fiber reinforced plastics to manufacture spacecraft such as satellites and rockets has high mechanical strength and low mass, which can save a lot of fuel. During the 1999 war in Kosovo, NATO used graphite bombs to knock out much of the country's electricity supply by creating a cloud of carbon fiber over a large area. These conductive fibers short-circuited the power supply.

At present, people can not directly use carbon or graphite to draw carbon fiber, can only use some carbon-containing organic fibers (such as nylon silk, acrylic silk, rayon, etc.) as raw materials, organic fibers and plastic resins together, placed in the atmosphere of rare gases, under a certain pressure strong heat carbonization into carbon fiber is a fibrous carbon material. The carbon content in its chemical composition is more than 90%. Because the simple substance of carbon cannot be melted at high temperatures (sublimation above 3800K), and is insoluble in various solvents, so far it is impossible to use the simple substance of carbon to make carbon fiber. Carbon fiber can be produced by solid phase carbonization of polymer organic fibers or gas phase pyrolysis of low molecular hydrocarbons. At present, the vast majority of carbon fibers produced and sold in the world are made of solid phase carbonization of polyacrylonitrile fibers. Its production step is A pre-oxidation: heating in the air, maintained at 200-300 degrees for tens to hundreds of minutes. The purpose of preoxidation is to transform the linear molecular chain of polyacrylonitrile into a heat-resistant ladder structure, so that it will not melt and not burn during high temperature carbonization and maintain the fiber state. B Carbonization: heated to 1200-1600 degrees in an inert atmosphere, maintained for a few minutes to tens of minutes, the product carbon fiber can be generated; The inert gas used can be high-purity nitrogen, argon, or helium, but high-purity nitrogen is generally used. C graphitization: heating to 2000-3000 degrees in an inert atmosphere (generally high purity argon) for a few seconds to tens of seconds; The resulting carbon fiber is also called graphite fiber. Carbon fiber has excellent densification (one of the representations of densification is the number of grams of fiber 9000 meters long), generally only about 19 grams; Tension up to 300KG/MM2; There are also a series of excellent properties such as high temperature resistance, corrosion resistance, electrical conductivity, heat transfer, and small expansion coefficient. Few other materials currently have as many excellent properties as carbon fiber. At present, carbon fiber is mainly made into carbon fiber reinforced plastics for application. This reinforced plastic is superior to steel and fiberglass, and has a wide range of uses, such as making important materials such as rockets and spacecraft; Making jet engines; Manufacture corrosion resistant chemical equipment. Badminton: Most badminton racket sticks are now made of carbon fiber. Inorganic polymer fibers containing more than 90% carbon. Among them, the carbon content of more than 99% is called graphite fiber. Carbon fiber has high axial strength and modulus, no creep, good fatigue resistance, specific heat and electrical conductivity between non-metal and metal, small thermal expansion coefficient, good corrosion resistance, low fiber density, and good X-ray transmission. However, its impact resistance is poor, easy to damage, oxidation occurs under the action of strong acids, and metal carbonization, carburizing and electrochemical corrosion occur when it is combined with metal. Therefore, the surface of carbon fiber must be treated before use. Carbon fiber can be carbonized with polyacrylonitrile fiber, asphalt fiber, viscose silk or phenolic fiber. According to the state, it can be divided into filament, staple fiber and staple fiber. According to mechanical properties are divided into general and high performance type. The strength of the universal carbon fiber is 1000 MPa and the modulus is about 100GPa. High-performance carbon fiber is divided into high-strength type (strength 2000MPa, modulus 250GPa) and high model (modulus 300GPa or more). Strength greater than 4000MPa is also known as ultra-high strength type; A model with a modulus greater than 450GPa is called a superhigh model. With the development of the aerospace and aviation industry, there has also been the emergence of high-strength high-elongation carbon fiber, whose elongation is greater than 2%. The largest amount is polyacrylonitrile based carbon fiber. Carbon fiber can be processed into fabric, felt, mat, tape, paper and other materials. In addition to being used as thermal insulation materials, carbon fiber is generally not used alone, and is mostly added to resins, metals, ceramics, concrete and other materials as reinforcement materials to form composite materials. Carbon fiber reinforced composite materials can be used as aircraft structural materials, electromagnetic shielding deelectrics, artificial ligaments and other body substitute materials, as well as for the manufacture of rocket shells, motor boats, industrial robots, automotive plate springs and drive shafts. Carbon fiber is made of polyacrylonitrile fiber, asphalt fiber or viscose fiber by oxidation, carbonization and other processes to produce carbon content of more than 90% of the fiber.

Carbon fiber has also made new contributions in replacing the core heating element of heating materials. Abroad, the core heating element of many energy-saving heating equipment has been gradually upgraded from the previously commonly used metal materials to carbon fiber materials. The application of carbon fiber materials in heating mainly considers the use of corrosion resistance, oxidation resistance (metal easily oxidized to cause local breakdown), high stability. Long life (many products can generally reach a stable working time of 100,000 hours at 300 degrees Celsius), high thermal conversion rate (more than 97%) and other characteristics. Because China is still relatively backward in the production and development of carbon fiber materials, high-quality carbon fiber materials still rely on imports from Japan and South Korea, so the price remains high, but with the emergence of domestic joint ventures and cooperation forms, products with carbon fiber as the core technology have entered the homes of ordinary consumers.

The application of carbon fiber products in heating is divided into many forms, such as staple fiber, staple fiber is usually used in heating products such as "carbon crystal" and "floor heating film", graphite products are widely used in early heating film, film products in addition to heating applications, in water heaters, industrial equipment constant temperature environment protection is also very widely used.

Carbon fiber can be processed into fabric, felt, mat, tape, paper and other materials. In addition to being used as thermal insulation materials, carbon fiber in traditional use is generally not used alone, and is mostly added to resins, metals, ceramics, concrete and other materials as reinforcement materials to form composite materials. Carbon fiber reinforced composite materials can be used as aircraft structural materials, electromagnetic shielding deelectrics, artificial ligaments and other body substitute materials, as well as for the manufacture of rocket shells, motor boats, automobiles, sports equipment, industrial robots, automotive plate springs and drive shafts. Carbon fiber is also widely used in military and civilian fields, for example, carbon fiber heating products, carbon fiber heating products, carbon fiber far-infrared physiotherapy products are also more and more into ordinary people's families. In addition, the country's power grid cables are also applied to carbon fiber materials.

Carbon fiber and steel are both commonly used in structural materials, and their strength is very different.

First, let's look at the strength of carbon fiber. Carbon fiber is composed of fibrous carbon elements and has the characteristics of light weight and high strength. In contrast, steel is made up of iron and other elements, which are relatively heavy and strong. Although carbon fiber is much less dense than steel, its strength is excellent. Carbon fiber is more than five times stronger than steel, and can even reach 10 times stronger under certain conditions. This makes carbon fiber in aerospace, automotive, sports equipment and other fields have a wide range of application prospects.

Second, the strength of carbon fiber is not limited to static load performance. In contrast, steel may be stronger under static load, but carbon fiber shows a greater advantage under dynamic load. This is because carbon fiber has good fatigue strength and impact energy absorption properties, which can effectively resist external shocks and vibrations. Therefore, carbon fiber is widely used in the aerospace and automotive fields, because these fields require high fatigue and impact properties of the material.

It is worth mentioning that although carbon fiber has high strength, its cost is relatively high. In contrast, the production cost of steel is relatively low, and it is easier to mass produce. This is one of the reasons why steel is still used in some projects with high cost requirements, such as construction.

When choosing materials, we need to consider factors such as strength and cost. If we pursue lightweight and high-strength requirements, and have enough budget, carbon fiber is a good choice. It can reduce the weight of the structure and improve the overall performance. For projects with larger cost constraints, steel is a more economical and practical choice.

All in all, there are clear differences in strength between carbon fiber and steel. Carbon fiber has the advantages of light weight and high strength, and has good fatigue and impact properties, and is widely used in high-tech fields. Steel, on the other hand, has the advantage of higher static load strength and low cost, which has a greater advantage in some cost-sensitive projects. Therefore, we need to make a wise choice according to the specific use needs, considering the performance and cost of materials.